Touch panels are input devices installed on image display devices in which at least a portion thereof that overlaps with the image display device is transparent.
A known example of a touch panel is a resistive film type touch panel. In a resistive film type touch panel, a stationary electrode sheet and a movable electrode sheet, in which a transparent electrode is formed on one side of a transparent base, are arranged so that the transparent electrodes are mutually opposed. An indium-doped tin oxide film (to be referred to as an ITO film) has widely been used for the transparent electrode of these electrode sheets.
A sheet in which an ITO film is formed on one side of a transparent base (to be referred to as an ITO film forming sheet) has low flexibility and is easily immobilized, thereby making it preferable for use as a stationary electrode sheet of an image display device. However, in the case of using as a movable electrode sheet on the side of an input operator of a touch panel, it had the problem of low durability during repeated deflection.
Therefore, a flexible sheet in which is formed a conductive coating film containing a π-conjugated conductive polymer (to be referred to as a conductive polymer film forming sheet) is used on one side of a transparent base as a movable electrode sheet on the side of an input operator of a touch panel.
However, in the case of using an ITO film forming sheet as a stationary electrode sheet on the side of an image display device and using a conductive polymer forming sheet as a movable electrode sheet on the side of a key operator of a touch panel, namely in the case of connecting mutually different conductors, contact resistance increased resulting in problems such as decreased input sensitivity and delays in coordinate input time.
In order to solve these problems, Patent Document 1 proposes the addition of metal ions to a conductive coating film containing a π-conjugated conductive polymer. In addition, Patent Document 4 proposes the addition of a conductive metal oxide in the form of indium oxide or tin oxide to an aqueous solution containing a π-conjugated conductive polymer and polyanions followed by coating the resulting solution onto a transparent base to form a transparent electrode.
In addition, the addition of metal particles to a conductive coating film containing π-conjugated conductive polymer has also been devised. Examples of electrode sheets in which metal particles have been added to a conductive coating film containing a π-conjugated conductive polymer are disclosed in Patent Documents 2 and 3.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2007-172984
[Patent Document 2] Japanese Laid-Open Patent Application No. 2005-327910
[Patent Document 3] Japanese Laid-Open Patent Application No. 2007-080541
[Patent Document 4] Japanese Laid-Open Patent Application No. 2006-286418